Several interactive displays are known in the prior art. For example, a user interface platform was developed in the MIT Media Lab, as reported by Brygg Ullmer and Hiroshi Ishii in “The metaDESK: Models and Prototypes for Tangible User Interfaces,” Proceedings of UIST 10/1997:14-17. This article describes how the metaDESK includes a near-horizontal graphical surface that is used to display two-dimensional (2D) geographical information. A computer vision system inside the desk unit (i.e., below the graphical surface) includes infrared (IR) lamps, an IR camera, a video camera, a video projector, and mirrors. The mirrors reflect the graphical image projected by the projector onto the underside of the graphical display surface to provide images that are visible to a user from above the graphical display surface. The article further teaches that the IR camera can detect a reflection from the undersurface of passive objects called “phicons” that are placed on the graphical surface. Thus, the IR camera detects an IR reflection from an IR reflective material applied to the bottom of a “Great Dome phicon” when the phicon is placed on the graphical surface and responds by displaying a map of the MIT campus on the graphical surface, with the actual location of the Great Dome in the map positioned where the Great Dome phicon is located. There is no discussion of details involved in detecting an object based upon the IR reflection, or in determining how to compensate for IR light in the ambient that might adversely effect the detection of a phicon using IR light reflected from the phicon.
A similar technique for sensing objects on a display surface is disclosed in several papers published by Jun Rekimoto of Sony Computer Science Laboratory, Inc., in collaboration with others. These papers briefly describe a “HoloWall” and a “HoloTable,” both of which use IR light to detect objects that are proximate to or in contact with a display panel on which a rear-projected image is visible. The rear-projection panel, which is vertical in the HoloWall and horizontal in the HoloTable, is semi-opaque and diffusive, so that objects reflecting IR light back through the panel become more clearly visible to an IR camera as they approach and then contact the panel. The system can thus detect a user's fingers or hand, or other objects. Again, these papers fail to discuss the effects on ambient IR light on sensing IR light reflected from objects to detect the object and do not mention any approach for controlling the intensity of the IR light used for sensing objects in response to the ambient IR light level.
It is important to either substantially exclude ambient IR light that might interfere with the detection of an object on an interactive display surface, like those discussed above, or to ensure that the intensity of IR light from an intended IR light source is greater than that of ambient IR light. If the ambient IR light source has a greater intensity when sensed to detect an object, it will substantially preclude the accurate detection of an object placed on a display surface. While the shape of an object placed on an interactive display surface might be detected based upon the shadow that it casts relative to a bright ambient light source disposed behind the object, the details of the object and any IR reflective shape or pattern applied to the object will not be evident. A bright ambient IR light source will effective wash out the reflection from an object placed on an interactive display surface and will thus interfere with the IR vision detection system and its ability to sense the location of an object on the display surface and other distinctive information that is conveyed by the reflected IR light from an intended IR source that is disposed on an opposite side of the display surface from the IR ambient light source. An incandescent light bulb of only 60 watts that is only a few feet from the interactive display surface may prevent an IR vision system from working properly to detect objects on the interactive display surface.
It might seem that an easy solution to this problem is simply to set the intended IR light source at its maximum possible IR output level. However, there may be undesired consequences to this action, since too high an IR light level produced by the intended IR source can adversely affect the operation of other devices that use IR light, such as remote controls. Instead, it would be preferable to control the IR light source used in an interactive display device so that the level of IR light it produces is greater than the ambient IR light level, but not excessively greater. While alternative approaches can be used for compensating for IR light in the ambient, it would be desirable to dynamically control the intended IR light sources used by actually sensing the IR light produced by the intended light sources and comparing with the level of the ambient IR light level in order to control the IR light sources.